In recent years, display apparatuses provided with a functional substrate such as a touch panel, a decorative panel and the like have been widespread. A touch panel is an input interface component. A decorative panel is, for example, a reinforcement glass printed for decoration, from the viewpoint of design, display surface protection and so forth.
Typically, in the case where the display apparatus is provided with the functional substrate, it is so configured that an air space is interposed between the display panel and the functional substrate so that a gap is provided between the display panel and the functional substrate. More specifically, in the case where the peripheral border of the display panel is bonded to the peripheral border of the functional substrate for example, the display panel and the functional substrate are bonded together with a space provided in between so that the display surface of the display panel is not in contact with the functional substrate. In the description below, such bonding of the display panel or the like and the functional substrate with the air space interposed between them is called “air gap bonding,” while the structure of the display apparatus in which the display panel or the like and the functional substrate are bonded together with the air space interposed between them is called an “air gap bonding structure.”
In the case where, for example, the functional substrate is a touch panel, the air gap bonding structure may be employed to avoid a display failure caused by the touch panel making contact with the display panel, even if the touch panel is warped toward the display panel as a result of pressing action by the user. In the description below, the display failure caused by such contact is referred to as “display unevenness.”
Japanese Patent Application Laid-Open No. 2004-117646 discloses a display apparatus having an air gap bonding structure, in which a display panel or the like and a functional substrate are bonded together with a thick double-sided tape so as to have an air space while separating the display panel from the functional substrate by a predetermined distance. In the case of using a double-sided tape, however, the following problems remain.
First, the bonding work using the double-sided tape is carried out manually in large part, since it is difficult to automate such work by a machine. Moreover, different products of double-sided tapes have different shapes, which requires the double-sided tape to be molded into a desired shape with the use of a dedicated punching die. In the case of bonding with the double-sided tape, therefore, problems arise in the productivity, manufacturing cost and so forth.
Second, the double-sided tape is generally configured with foam material such as acrylic foam having a certain thickness that is held between adhesive layers in order to secure a desired distance between the display panel and the functional substrate. However, foam material such as acrylic foam is softer than non-foam material such as synthetic resin, and therefore easily causes bulk destruction. Thus, the double-sided tape tends to have lowered adhesion strength per unit area because of the bulk destruction.
Third, in the case where the size of the display apparatus is increased, a wide double-sided tape is necessary, making it difficult to attain a slim border display.
In order to solve the problems described above, it is conceivable to employ an adhesive made of resin in place of a double-sided tape. In particular, the adhesive made of resin is inexpensive, and also has the advantage of facilitating an automated bonding work. In the case where the adhesive made of resin is applied to the air gap bonding structure, however, the following problems arise.
First, the adhesive made of resin has low resistance to weight. Accordingly, it is difficult for the adhesive made of resin to maintain the distance between the functional substrate and the display panel.
Second, in the case where the viscosity of the adhesive is made higher in order to improve the resistance to weight, the discharging performance of a dispensing device, which is to be used for example to apply the adhesive, is significantly lowered. Moreover, in the case where spacer material is mixed into the adhesive in order to keep the space between the functional substrate and the display panel after bonding, the nozzle of the dispensing device is easily clogged. Thus, the countermeasures as described above would deteriorate the productivity.
It is therefore difficult to maintain the distance between the display panel and the functional substrate if the adhesive made of resin is used as it is in place of a double-sided tape.
Japanese Patent Application Laid-Open No. H07-28409 discloses an air gap bonding structure in which a protective plate is bonded to a liquid crystal panel by a spacer made of elastic resin and adhesive resin. The spacer includes elastic resin having the shape of a long and thin quadrangular prism and adhesive resin located on three side surfaces of the elastic resin. The protective plate and the liquid crystal panel are bonded together by being adhered to one side surface of elastic resin and to the opposite side surface of the one side surface, respectively. Thus, the distance between the protective plate and the liquid crystal panel is maintained by the elastic resin.
To bond the protective plate to the liquid crystal panel by the spacer described above, however, it is necessary to carry out complicated steps of applying adhesive resin to the side surfaces of elastic resin and then adhering the protective plate and the liquid crystal panel to the side surfaces of the elastic resin. Therefore, the invention according to Japanese Patent Application Laid-Open No. H07-28409 cannot serve to solve the problems of productivity and so forth.